NA plus /K plus /CL--COTRANSPORTER MEDIATED RB plus FLUXES IN MEMBRANE-VESICLES FROM KIDNEYS OF NORMOTENSIVE AND HYPERTENSIVE RATS

This paper describes experiments to examine Rb+ fluxes via the Na+/K+/Cl- cotransporter in membrane vesicles from renal outer medulla of three strains of rat: (A) Wistar (B) Milan hypertensive (MHS) and normotensive (MNS), and (C) Sabra salt-sensitive hypertensive (SBH) and salt-resistant (SBN). Initially, Na+-dependent furosemide- or bumetanide-inhibited 86Rb+ fluxes were characterised using Wistar rat microsomes. The latter were partially purified on a metrizamide cushion, and assay conditions were optimized for use with microsomes from the other rats. The major result is that in microsomes from adult Milan hypetensive (MHS) rats the rate of the Na+/K+/Cl--cotransporter mediated 86Rb flux at sub-saturating concentrations of Rb, appears to be significantly greater than in the normotensive (MNS) controls. The effect reflects an increased apparent Rb affinity of the cotransporter in MHS microsomes. There is no difference in maximal rate or in the apparent Na+ activation affinity of the 86Rb+ flux. In addition bumetanide appears to be a somewhat more effective inhibitor in MHS compared to MNS microsomes. The 86Rb+ flux result is compatible with a previous finding that in red cells, Na+/K+-cotransporter mediated fluxes are increased in MHS compared to MNS. It supports the notion that the Na+/K+/Cl--cotransporter in both red cells and kidney is a genetic marker for hypertension. It is of interest that apparetly more than one Na+ transport system is affected in MHS hypertensive kidneys (a) the Na+/K+/Cl- cotransporter i nthe thick ascending limb of Henle and (b) the Na+/H+ exchanger and/or a conductive Na+-pathway in brush-border membranes from proximal tubule. It is conceivable that in the hypertensive animals a common regulatory pathway (e.g., phosphorylation) or protein (e.g., cytoskeleton) is affected along the length of the nephron. In Sabra SBH and SBN rat microsomes, no difference was found for the 86Rb+ flux via the Na+/K+/Cl- cotransporter (or via a K+ channel). © 1990.